M Manser Invicta Grammar School GCSE PHYSICS P2a : Collecting energy from the sun Photocells By the end of this presentation you should be able to: 1.Describe that photocells transfer light into electricity; produce direct current; can operate in remote locations; have a power that depends on the surface area exposed to sunlight.photocells 2.Describe some advantages and disadvantages of using photocells to provide electricity:using photocells to provide electricity 3.Describe how light produces electricity in a photocellhow light produces electricity in a photocell

What is a photocell? A photocell can also be called a solar cell. It is a flat plate that is made out of silicon (a semi- conducting material) and placed in a position that allows sunlight to fall on it. Photocells convert light energy to electrical energy. They are connected to circuits to provide a current that flows in one direction only (d.c.)

Factors affecting the output of a solar cell The size of the area that can absorb the light. The larger the area, the more electrons that can be released; so a larger current will flow. This means more electrical energy is produced. The time of day also affects the output. When the sun appears close to the horizon morning and evening), less light energy will reach the photocell because of how much more of the atmosphere the sunlight must pass through. When the sun appears directly overhead, the distance travelled through the atmosphere is smallest. The intensity of sunlight reaching the photocell is highest, and the most electricity will be produced at this time. (see animation following)

EARTH atmosphere A solar panel When the sun appears close to the horizon… …the distance travelled through the atmosphere… …is greater than when the sun appears directly overhead. The intensity of the light reaching the photocell is highest around mid-day to 1pm. This is when the least energy is absorbed by the atmosphere. 7am 7pm (summer winter) Power output

How do photocells turn light into electricity? This shows a really magnified view of the cross section of the silicon in the photocell. The photocell is connected to a circuit. The silicon atoms…. …all have electrons which are held quite tightly. When sunlight hits the photocells, the electrons use the energy to break free. The electrons then flow in the circuit in one direction continuously ie a direct current flows.

Many electrons may be released at the same time depending on how much of the silicon atoms are exposed to sunlight.